<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>my css3</title>
    <style>
        .c1 {
            margin: 0 auto;   /*上下为0，左右自动，则居中*/
            width: 580px;
            height: 435px;
            border: 1px dashed gray;
        }
        #id1 {
            display: none;   /*不显示*/
        }
        .c1:hover #id1 {   /*鼠标悬停在.c1上时id1的样式*/
            display: block;
        }
    </style>
</head>
<body>
<div class="c1">
    <img id="id1" src="https://img01.sogoucdn.com/app/a/100520021/6b859fc50465b1f155ed28ab07e1353b">
</div>
</body>
</html>